1. Field of the Invention
This invention relates to a detector device in which a mixing ratio of such as, for example, gasoline and alcohol is optically measured, and suited in use for fuel of internal combustion engine.
2. Description of the Prior Art
In an internal combustion engine for motor vehicle, it has been suggested to apply a mixing liquid of gasoline and alcohol to a combustible fuel. In order to obtain a good engine output, it is necessary to continuously detect a mixing ratio of the liquid so that an automatic combustion control unit may work to insure most appropriate quantity of injection fuel.
For this purpose, a detector device is provided which comprises an optical permeable column arranged its outer whole surface to be in direct contact with a mixing liquid of gasoline and alcohol. Sight beams from a light emitting diode permeate the column through its one end and reach at a boundary between the column and the mixing liquid. The light beams incident on the boundary at less than a critical angle, is totally refracted while the light beams incident on the boundary at more than a critical angle, is totally reflected. The light beams totally reflected, go out of the column through its other end to fall on a photo diode, the output of which is in accordance with the quantity of the light beams fell upon. Since the critical angle changes depending upon the mixing degree of the liquid, measuring the output from the photo diode enables to obtain a mixing ratio of the liquid.
The device, however, places both the diodes to sandwich the column in the lengthwise direction, requiring cases to enclose those diodes discretely, and making a whole structure greater, and increasing the number of assembly processes.
Therefore, it is an object of this invention to provide a detector device which is capable of reducing a thickness and lengthwise dimension to make a whole structure compact, and cost saving, contributing to decrease of assembly processes.
According to the present invention, there is provided a detector device comprising; an optically permeable plate, one side of which is placed to be in direct contact with mixing liquid of different kinds of components; a light emitting diode located at other side of the optically permeable plate to be opposite to the mixing liquid, so that light beams emitted from the diode enter the optically permeable plate to be incident on a boundary between the plate and the mixing liquid, the light beams incident on the boundary at less than a critical angle being refracted toward the mixing liquid, while the light beams incident on the boundary at more than the critical angle being totally reflected, the critical angle depending on a degree of the mixing liquid; a photo diode having a rectangular shape, and located in coplanar relationship with the light emitting diode to receive the light beams totally reflected from the boundary to generate an output in accordance with the light beams received; and
the distance between the photo diode and the light emitting diode and width dimension of the photo diode along the direction of the distance being determined such as to provide incident angles ranging from a minimum corresponding to the critical angle when the mixing liquid ratio is at lower limit of the predetermined range to a maximum corresponding to the critical angle when the mixing liquid ratio is at upper limit of the predetermined range.